I did this job quite a while ago and I have CRS disease (Can't Remember Shiit). But I seem to recall there are 2 threaded studs on a strap that's molded into the cushion, but only 1 stud uses a speed-nut, the other just sticks into a hole in the bumperette that has this little metal insert thingy that promotes a force fit.
Don't screw up your bumber on my account, but that's what I vaguely recall.
strike
(I'll look at my parts book and I know I have some new cushions somewhere in the basement. If I see something enlightening I write back.)